CN114375367A

CN114375367A - Device and method for exhaust gas aftertreatment and use thereof

Info

Publication number: CN114375367A
Application number: CN202080061797.XA
Authority: CN
Inventors: 罗伯特·史泽洛克; 亚历山大·萨斯多夫; 佛罗莱恩·瑞米勒
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2019-07-15
Filing date: 2020-07-15
Publication date: 2022-04-19
Also published as: JP7462730B2; KR20220031912A; US20220259998A1; EP3999726A1; DE102019210413B4; WO2021009240A1; JP2022541211A; DE102019210413A1

Abstract

The invention relates to a method for exhaust gas aftertreatment, comprising the following steps: a) providing raw exhaust gas containing nitrogen oxides, b) introducing the raw exhaust gas containing nitrogen oxides into a catalytic evaporator (1), c) introducing fuel into the catalytic evaporator (1), thereby obtaining a converted fuel, d) mixing urea with the converted fuel; and e) feeding the mixture obtained after step d) to an exhaust gas aftertreatment system (8). The invention further relates to a device for exhaust gas aftertreatment and to the use thereof.

Description

Device and method for exhaust gas aftertreatment and use thereof

Technical Field

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine; the use of a catalytic evaporator in such a process; an apparatus for exhaust gas aftertreatment, which apparatus is particularly suitable for carrying out the method according to the invention; and to the use of such a device for exhaust gas aftertreatment.

Background

Exhaust gas aftertreatment refers to the process of cleaning combustion gases by mechanical, catalytic or chemical means after they leave the combustion space or chamber of an internal combustion engine. In order to reduce nitrogen oxides (NOx) with Selective Catalytic Reduction (SCR) technology, a catalyst and a reducing agent, such as ammonia, are used. For this purpose, an aqueous urea solution is injected from which ammonia gas is generated by pyrolysis and hydrolysis during further transport through the exhaust pipe. The three-way catalyst can be used for reducing hydrocarbon and carbon monoxide.

The effectiveness of catalytic exhaust gas aftertreatment, i.e. the conversion or conversion, depends, inter alia, critically on the operating temperature. Virtually no reaction takes place below about 250 ℃. This is why even modern vehicles have a high pollutant emission after a cold start. In this operating state, the catalyst has not yet reached the operating temperature and therefore the conversion of the emitted pollutants is insufficient.

There are strategies to rapidly increase the exhaust gas temperature. For example, the catalyst may be placed in the exhaust system near the engine. However, at least in the case of gasoline engines, there is the risk that the temperature becomes too high in other operating states, for example close to the rated power. Since temperatures of 1000 ℃ destroy the catalyst. Good conversion and long service life are obtained at 400 ℃ to 800 ℃. Alternatively, the exhaust gas temperature may be increased by an electric heater or by post injection inside the engine and/or in the exhaust train.

However, these measures have the following effects: further increases consumption and generates additional emissions after cold start.

Disclosure of Invention

Starting from the prior art, the object of the invention is therefore: an exhaust gas aftertreatment is provided, optionally including selective catalytic reduction, which enables catalytic conversion at lower temperatures.

According to the invention, this object is achieved by a method for exhaust gas aftertreatment according to claim 1, by a use according to claim 8, by a use according to claim 15 and by an apparatus according to claim 9. Advantageous developments of the invention can be found in the dependent claims.

According to the invention, a method for the aftertreatment of exhaust gases, in particular for removing nitrogen oxides, is proposed, comprising the following steps:

a) providing a raw exhaust gas containing nitrogen oxides,

b) introducing the raw exhaust gas containing nitrogen oxides into a catalytic evaporator,

c) introducing fuel into the catalytic evaporator, thereby obtaining a converted fuel,

d) mixing urea with the converted fuel; and

e) conveying the mixture obtained after step d) to an exhaust gas aftertreatment system.

Changing the composition of the fuel by evaporation of the fuel in step c). In particular to generate H₂And/or CO and/or hydrocarbons, such as short chain hydrocarbons having 1 to 10 carbon (C) atoms, wherein, in some embodiments of the invention, 1 to 5 carbonsThe atomic components account for a large proportion of (>66％)。

Advantageously, in step e), the heat of catalytic evaporation is used for the evaporation and conversion (pyrolysis and hydrolysis) of the urea. The method can be used when the exhaust gas contains nitrogen-oxygen compounds. In this regard, controlled systems are contemplated. In the engine map point, in which nitrogen oxides are increasingly contained in the exhaust gas, the controlled system is switched on. The system is not effective at other engine map points where small or tolerable amounts of nitrogen oxides are produced by combustion. If it is not active, the delivery of air and exhaust gases is stopped.

The raw exhaust gas containing nitrogen oxides may be untreated raw exhaust gas. It may also be a treated raw exhaust gas, which is treated, for example, with a fine dust filter and/or a diesel oxidation catalyst.

Steps b) and c) may be performed simultaneously. In step e), the mixture can be conveyed directly into the exhaust gas aftertreatment system or by introducing it into the exhaust gas line leading from the engine to the exhaust gas aftertreatment system.

The method according to the invention has been developed on the basis of catalytic evaporation technology known per se, wherein the raw exhaust gases of the engine containing nitrogen oxides, liquid fuel and urea solution are used. Heat is generated within the system by the catalytic conversion of fuel in the catalytic vaporizer. In this way, the system is substantially independent of the operation of the engine. It is thus possible to: the reducing agent is produced from the aqueous urea solution without being influenced by the engine operation, in particular the exhaust gas temperature and the exhaust gas mass flow. Furthermore, in the method according to the invention, hydrogen and hydrocarbons, such as acetylene, are produced from the added fuel, which are used as additional reactants, i.e. reducing agents, in Selective Catalytic Reduction (SCR) systems for exhaust gas Aftertreatment (AGN).

The amounts of urea solution and fuel provided are the usual amounts used in the operating mode of the catalytic evaporator known per se.

The raw exhaust gas containing nitrogen oxides fed to the catalytic evaporator can be a part of the normal engine exhaust gas, i.e. a part can be separated from the engine exhaust gas stream and provided in step a) as raw exhaust gas containing nitrogen oxides, which raw exhaust gas is introduced into the catalytic evaporator. This division can be achieved by flaps or slides in the waste line, which can be actuated accordingly. The raw exhaust gases can also be led directly from the engine and supplied to the catalytic evaporator.

With the method according to the invention it is advantageously achieved that: as opposed to heating the entire exhaust gas stream according to the prior art, only a small partial stream of the raw exhaust gas containing nitrogen oxides needs to be heated. Additional heat is also generated by the conversion of the fuel, which additional heat does not have to be introduced electrically. For catalytic conversion, only the catalyst needs to be heated. The reaction can be controlled by varying the reactant flow.

Catalytic evaporators can be used in the process according to the invention, since they are known per se from the prior art. The expert also knows how to operate them in principle. An example of a catalytic evaporator which can be used in the method according to the invention is described in DE102015120106Al, to which full reference is made with regard to design details and operating mode.

The catalytic evaporator used in the process according to the invention can have a catalyst, which can be applied, for example, to a support. The catalyst-bearing support may be placed in a reaction vessel such that an intermediate void is formed between the inner surface of the reaction vessel and the catalyst surface.

In operation of the catalytic evaporator, for example, liquid fuel can be added to the inside of the reactor wall of the catalytic evaporator, while an oxidant, for example air, is supplied to the catalyst side. A small portion of the fuel is oxidized on the catalyst and the heat generated therein is used to completely vaporize the fuel. Heat transfer is primarily by thermal radiation from the hot catalyst surface to the fuel surface. The reactor wall on which the fuel is applied is here cooler than the fuel itself. No deposits or encrustations were formed at all.

The raw exhaust gas comprising nitrogen oxides supplied in step a) may contain residual oxygen. If the concentration of residual oxygen in the original exhaust gas is sufficient, this may be sufficient as an oxidant for the operation of the catalytic vaporizer. If the concentration of residual oxygen in the raw exhaust gas containing nitrogen oxides is too low, then in one embodiment, the oxidant may be further introduced into the catalytic vaporizer in step c). This oxidant is an additional oxidant in the original exhaust gas in addition to residual oxygen. This oxidizing agent may be oxygen or an oxygen-containing medium, in particular air. The amount of oxidant can be selected such that the usual amount of oxidant in the catalytic vaporizer is reached. The air can come from the environment and, if necessary, can be loaded by a turbocharger.

The mixture formed after step d) can have hydrogen (H)₂) As a reducing agent. In addition, the mixture may also have NH₃CO, hydrocarbons such as acetylene, and mixtures thereof.

By varying the reactant streams of fuel, urea solution, nitrogen-containing raw exhaust gas, and possibly oxidant, a separate reductant may be provided according to the operating point in the engine map. The provision of such a reducing agent in the method according to the invention increases the activity of the SCR system, thereby enhancing the reduction of nitrogen oxides in the engine exhaust. This advantage is particularly effective in cold starts and other operating points with cold exhaust after-treatment systems.

In one embodiment, the exhaust gas aftertreatment system may include equipment for pyrolysis and hydrolysis, such as a hydrolysis catalyst, and equipment for Selective Catalytic Reduction (SCR). Such devices are known per se, and the skilled person therefore knows how they are constructed and how they can be operated. It has proven advantageous for the method according to the invention to: the apparatus for pyrolysis and hydrolysis and the apparatus for SCR are installed in housings separated from each other. In this way it is possible to: these apparatuses, in particular apparatuses for hydrolysis, are used in a particularly suitable location in the process according to the invention. The device for pyrolysis and hydrolysis, the hydrolysis catalyst, can be located in the exhaust gas partial stream as well as in the main exhaust gas stream.

In some embodiments, the urea may be used in the form of a urea solution, such as an aqueous urea solution, particularly a 32.5% urea solution. This has proven to be particularly suitable for exhaust gas aftertreatment systems.

In one embodiment, the mixing of the urea solution with the evaporated fuel may be performed upstream of the exhaust system or in the exhaust system. In the process according to the invention, the mixture from step d) is introduced into an exhaust gas aftertreatment system. This can be done by introducing this mixture into the exhaust system connecting the engine to the exhaust aftertreatment system. The urea solution, which can be evaporated if necessary, can be mixed with the evaporated fuel before being supplied into the exhaust system and/or within the exhaust system.

In another embodiment, the mixture from step d) may be first fed to a plant for hydrolysis and the product thus obtained may be subsequently fed to a plant for SCR.

In another embodiment, exhaust gas aftertreatment, including selective catalytic reduction if necessary, may be operated already at a temperature of about 170 ℃ or about 180 ℃ or about 190 ℃ or about 200 ℃. This means, therefore, that with the method according to the invention, exhaust gas aftertreatment can already be started and carried out at much lower temperatures than known from the prior art.

The method according to the invention can be used for converting nitrogen oxides for SCR systems of any type of internal combustion engine that is operated with an SCR system for reducing NOx emissions.

The subject matter of the invention is also the use of a catalytic evaporator as described in detail herein in a method according to the invention as also described in detail above.

Furthermore, a reducing agent is provided, which can be obtained by the method according to the invention. With regard to the production method and components, reference is made to the above-described embodiments. In particular, the reducing agent comprises hydrogen, hydrocarbons, in particular ethylene, ammonia and/or carbon monoxide.

Furthermore, a device for exhaust gas aftertreatment is described, for example comprising an SCR, wherein the device comprises:

-a catalytic evaporator, the catalytic evaporator being,

-a raw exhaust gas inlet line to the catalytic evaporator adapted to introduce raw exhaust gas containing nitrogen oxides into the catalytic evaporator,

-a fuel inlet line to the catalytic evaporator, adapted to introduce fuel into the catalytic evaporator,

-an output line from the catalytic evaporator adapted to output evaporated fuel from the catalytic evaporator,

-a urea reservoir and a urea inlet line connected to a mixing space for mixing the evaporated fuel obtained in the catalytic evaporator with urea, if necessary, an

-an exhaust gas after-treatment system.

By the term "adapted" as used above, it is meant that the respective conduits are designed such that they can conduct the material transported therein without negative effects, i.e. they are, for example, inert with respect to the material to be conducted. Furthermore, the term "adapted to" also indicates that the respective line is connected to a reservoir with the material to be transported.

The device according to the invention is particularly suitable for carrying out the method according to the invention described above. The details of the design and the manner of operation of the device therefore also result from the above description of the method according to the invention.

In one embodiment, the exhaust gas aftertreatment system comprises a device for hydrolysis and a device for selective catalytic reduction known per se. The apparatus for hydrolysis may, for example, comprise a hydrolysis catalyst. The apparatus for selective catalytic reduction may have, for example, a catalyst for selective catalytic reduction. The device for hydrolysis and the device for selective catalytic reduction can be arranged in different housings. This can be achieved by: the devices according to the invention are built independently of one another at different locations of the devices, but can nevertheless be subjected to associated exhaust gas treatment. The device for hydrolysis can be located in the exhaust gas partial stream or in the main exhaust gas stream.

In one embodiment, the plant according to the invention may also comprise urea evaporationA vaporizer adapted to vaporize the urea solution prior to mixing the urea solution with the vaporized fuel. The advantage of urea solution evaporation and catalytic fuel evaporation is functional separation. This makes it possible to use the prior art in urea evaporation. These do not have to be coordinated but instead produce an improved reductant having NH₃(from urea), H₂CO/ethylene (from fuel).

In one embodiment, the space for mixing may be an outlet line and/or an exhaust system.

In one embodiment of the device according to the invention, the device can also have an oxidant feed line to the catalytic vaporizer, which is adapted to introduce the oxidant into the catalytic vaporizer. Such an oxidant, such as oxygen or air, may need to be fed if the original exhaust gas does not have the necessary concentration of residual oxygen.

The subject of the invention is also the use of a device as described above for the aftertreatment of exhaust gases comprising selective catalytic reduction.

By means of the device described above, the advantages achieved by the method according to the invention can be achieved in a simple and advantageous manner.

Drawings

The invention shall be explained in more detail below with the aid of the figures without limiting the general idea of the invention. Wherein:

fig. la, 1b show schematic diagrams of embodiments of an apparatus for exhaust gas aftertreatment;

FIG. 2 illustrates a view of an exemplary catalytic evaporator that may be used;

fig. 3 shows the principle of action of the catalytic evaporator of fig. 2.

Detailed Description

Fig. la schematically shows a device for exhaust gas aftertreatment with a catalytic evaporator 1, which is explained in more detail in fig. 3 and 4 below. The engine 10, for example a diesel engine, is used in the usual manner for the operation of a motor vehicle, wherein fuel and air supply to the engine takes place. The resulting raw exhaust gas containing nitrogen oxides is exhausted from the engine 10 through an exhaust train 9. These raw exhaust gases containing nitrogen oxides from the engine 10 are conveyed to the device 8 for exhaust gas aftertreatment. The device 8 for the exhaust gas aftertreatment has a device 81 for hydrolysis, for example a hydrolysis catalyst, and a device 82 for selective catalytic reduction. The means 81 for hydrolysis and the means for selective catalytic reduction are present in separate housings. At least a portion of the raw exhaust gas containing nitrogen oxides is removed from the exhaust gas system 9 via the raw exhaust gas supply line 2 and fed to the catalytic evaporator 1. Fuel is supplied to the catalytic evaporator 1 from a fuel accumulator 4 via a fuel supply line 3. If necessary, an oxidizing agent, for example air, can be supplied to the catalytic evaporator 1 via an oxidizing agent supply line 13. The fuel evaporated in the catalytic evaporator 1 is discharged from the catalytic evaporator 1 via a discharge line 7. Urea solution is led from the urea reservoir 5 via a urea inlet line 6 into an inlet line 7. The inlet line 7 functions as a mixing space 12 for mixing the evaporated fuel and the urea. The device 81 for hydrolysis is part of the exhaust gas aftertreatment system 8, which is separate from the device 82 for SCR. The device 81 for hydrolysis is located downstream of the space 12 for mixing and upstream of the exhaust gas system 9, while the device 82 for SCR is located downstream of the exhaust gas system 9 in a location after the mixture from the catalytic evaporator 1 is fed to the exhaust gas system 9.

Fig. lb shows a further embodiment of the device according to the invention. This corresponds to the apparatus shown in fig. la, wherein the apparatus 81 for hydrolysis is located in the exhaust gas system (main exhaust gas stream) 9.

Fig. 2 shows a catalytic vaporizer 1, how it is used in the method according to the invention. The catalytic vaporizer 1 has a catalyst 112 which is applied to a metal mesh 113. Such materials known from the prior art can be used here as catalyst 112 and metal mesh 113. A metal mesh 113 with catalyst 112 may be present in the reaction vessel 114. In fig. 2, for the sake of clarity it is shown as follows: the catalyst 112 together with the expanded metal 113 is pulled out of the reaction vessel 114. If the catalyst 112 is inserted into the reaction vessel together with the expanded metal 113, an intermediate gap is formed between the inner surface 115 of the reaction vessel 114 and the surface of the catalyst 112 on the expanded metal 113.

Fig. 3 schematically shows the operation of the catalytic evaporator shown in fig. 2. Fuel is added to the lower surface of the reaction vessel 114, while untreated raw exhaust gas and, if necessary, additional oxidizing agent are delivered to the catalyst side. A small portion of the fuel is oxidized at the catalyst 112 and the heat generated therein is used to completely vaporize the fuel. The heat transfer is primarily by thermal radiation from the hot surface of the catalyst 112 to the surface of the fuel film. The fuel-coated wall of the reaction vessel 114 can be cooler than the fuel itself. And therefore no deposits or encrustations are formed at all.

Of course, the invention is not limited to the embodiments shown in the figures. Accordingly, the foregoing description is not to be taken in a limiting sense, but is instead to be taken in an illustrative sense. The following claims should be read: the mentioned features are present in at least one embodiment of the invention. This does not exclude the presence of further features. If the description or claims define "first" and "second" features, this may help to distinguish between like features without specifying a priority order.

Claims

1. A method for exhaust gas aftertreatment, comprising the steps of:

a) providing a raw exhaust gas containing nitrogen oxides,

b) introducing the raw exhaust gas containing nitrogen oxides into a catalytic evaporator (1),

c) introducing fuel into the catalytic evaporator (1), thereby obtaining a converted fuel,

d) mixing urea with the converted fuel; and

e) conveying the mixture obtained after step d) to an exhaust gas aftertreatment system (8).

2. Method according to claim 1, characterized in that, in addition, an oxidizing agent is introduced into the catalytic vaporizer (1) in step c).

3. The method according to any one of claims 1 or 2, characterized in that the exhaust gas aftertreatment system (8) comprises a device (81) for hydrolysis and a device (82) for selective catalytic reduction.

4. A method according to any one of claims 1-3, characterized in that the urea is used in the form of a urea solution.

5. A method according to any one of claims 1-4, characterised in that the mixing of the urea with the evaporated fuel takes place before or in a part of the exhaust gas line (9).

6. The method according to any one of claims 1 to 5, the mixture from step d) being fed to the device for hydrolysis (81) and the product obtained thereafter being fed to the device for selective catalytic reduction (82).

7. The method of any one of claims 1 to 6, wherein exhaust gas aftertreatment can be operated at a temperature of about 170 ℃ or higher.

8. Use of a catalytic evaporator (1) in a method according to any one of claims 1 to 7.

9. An apparatus for exhaust gas after-treatment, the apparatus comprising:

a catalytic evaporator (1) for the catalytic evaporator,

a raw exhaust gas feed line (2) to the catalytic evaporator (1), which is suitable for introducing raw exhaust gas containing nitrogen oxides into the catalytic evaporator (1),

a fuel feed line (3) to the catalytic evaporator (1), which is suitable for introducing fuel into the catalytic evaporator (1),

an outlet line (7) from the catalytic evaporator (1) which is adapted to discharge evaporated fuel from the catalytic evaporator (1), and

an exhaust gas aftertreatment system (8).

10. Plant according to claim 9, further comprising a urea reservoir (5) and a urea inlet line (6) connected to a mixing space (12) for mixing evaporated fuel obtained in the catalytic evaporator and urea.

11. An arrangement according to claim 9 or 10, characterized in that the exhaust gas aftertreatment system (8) comprises an arrangement (81) for hydrolysis and an arrangement (82) for selective catalytic reduction.

12. The apparatus according to claim 11, characterized in that the apparatus for hydrolysis (81) and the apparatus for selective catalytic reduction (82) are present in separate housings from each other.

13. The apparatus according to any one of claims 9 to 12, characterised in that the mixing space (12) is the outlet line (7) and/or an exhaust gas system (9).

14. The apparatus according to any one of claims 9 to 13, characterized in that it also has an oxidant inlet line (13) to the catalytic evaporator (1) adapted to introduce an oxidant into the catalytic evaporator (1).

15. Use of an apparatus according to any of claims 9 to 14 for exhaust gas aftertreatment comprising selective catalytic reduction.